After David figures out that Bean is not the genius professor he is meant to be, they try to come up with a plan to just get them through the presentation - as it was David's decision to invite over a professor and he will be held accountable.
In the gallery, Bean is inspecting the painting and, just like another of the TV sketches they've re-used (when he was in the library with the old book), he sneezes on the painting - and when trying to clean it gets ink all over the face of Whistler's mother. He uses a cleaning agent - but the corrosive acid makes it even worse.
David freaks out, but they have no choice to lock it away - and get drunk.
Bean comes up with a plan - he returns to the gallery at night and replaces the painting with a poster. Using egg yolk and nail polish he adds a thin layer to the poster to make it look more authentic.
Next day, the crowd are ready for the big presentation - including the special guest General Newton (Burt Reynolds). They are all fooled by the poster - but Bean and David have forgotten about the big speech! George introduces him to the stage - Bean is terrified but pulls off a fine performance talking about the merits of 'family'. David and Bean are elated - and the movie should have ended here, but thankfully there's better stuff to follow...
David is taken aside by the police detective from before, and told that his daughter has been in a motorcycle accident. On route to the hospital, the detective needs to stop a guy with a gun in the middle of the street. We hear a gunshot.
David and Bean make it to the hospital. Still wearing his namebadge, Bean is mistaken for a proper doctor and dressed in scrubs. He soons founds out he needs to operate on a cop with gunshot wounds - which of course happens to be his enemy - the detective!
Using just his fingers, Bean removes the bullet (after earlier finding it while looking for an M&M he dropped into the wound).
Walking around the hospital, he is grabbed anonymously by David and asked to help his daughter, who is in a light coma. Left alone in the room, he mixes the paddles and lands on top of the patient who wakes up with a shock.
David and his wife race into the room - and Bean reveals himself. All he asks in return is to stay another week.
He enjoys the rest of his holiday - buying some dodgy presents for the family and taking some proper tourist trips around LA, all to a soundtrack of Randy Newman's "I love LA!".
Back home, Bean puts his ted to bed and looks up to the wall - to see the authentic, damaged, painting of Whistler's Mother hanging in all its glory!